1. Field of the Invention
The present invention relates to a method, system, and computer program product maintaining mirror and storage system copies of volumes at multiple remote sites.
2. Description of the Related Art
Disaster recovery systems typically address two types of failures, a sudden catastrophic failure at a single point in time or data loss over a period of time. In the second type of gradual disaster, updates to volumes may be lost. To assist in recovery of data updates, a copy of data may be provided at a remote location. Such dual or shadow copies are typically made as the application system is writing new data to a primary storage device. Different copy technologies may be used for maintaining remote copies of data at a secondary site, such as International Business Machine Corporation's (“IBM”) Extended Remote Copy (XRC), Peer-to-Peer Remote Copy (PRRC), Global Copy, and Global Mirror Copy. Geographically Dispersed Parallel Sysplex (GDPS™) is an end-to-end Resource Management automated solution that manages storage based data replication solutions, such as those mentioned above, as well as other resources such as servers and workloads. (GDPS is a registered trademark of IBM).
In data mirroring systems, such as PPRC and XRC, data is maintained in volume pairs in a consistency group. A volume pair is comprised of a volume in a primary storage device and a corresponding volume in a secondary storage device that includes an identical copy of the data maintained in the primary volume. Volumes in the primary and secondary storages are consistent when all writes have been transferred in their logical order, i.e., all dependent writes transferred first before the writes dependent thereon. A consistency group has a consistency time for all data writes in a consistency group having a time stamp equal or earlier than the consistency time stamp. A consistency group is a collection of updates to the primary volumes such that dependent writes are secured in a consistent manner. The consistency time is the latest time to which the system guarantees that updates to the secondary volumes are consistent. Consistency groups maintain data consistency across volumes and storage devices. Thus, when data is recovered from the secondary volumes, the recovered data will be consistent. In certain backup systems, a sysplex timer is used to provide a uniform time across systems so that updates written by different applications to different primary storage devices use consistent time-of-day (TOD) values as time stamps. Application systems time stamp data sets when writing such data sets to volumes in the primary storage. The time stamp determines the logical sequence of data updates.
To provide backup of data, a production volume may be mirrored to a backup production volume in the same local site by performing a mirror copy operation. To provide protection from a disaster, the data may also be mirrored to a geographically remote location. In this way, if the primary production volume fails, then the system can failover to using the backup production volume at the local site. However, if both local sites fail or experience a disaster, then production can switch over to the remote site mirror copy. Further, a production site may mirror data to multiple sites, including another local site and a remote site. The local site may further send a directive to the remote site to make a point-in-time copy of the remote site mirror copy. The local site may receive a directive to perform a point-in-time copy operation and forward that directive to the remote site to create a remote point-in-time copy from the remote mirror copy of the data.